1. Field of the Invention
The present invention generally relates to a flexible architecture Global Positioning System (GPS) receiver. The present invention also relates to a method for processing GPS signals which provides for the potential of simultaneous search and tracking of the GPS signals by the GPS receiver. The present invention further relates to using lossless multiplexing for allowing single channel receiver hardware to process multiple satellite signals, i.e., to behave as multi-channel receiver hardware, without any substantial performance degradation.
2. Description of the Related Art
One of the most demanding functions performed by a GPS receiver is signal acquisition. Traditional GPS receivers are implemented in a real-time mode in which each sampled bit of the input signal is processed sequentially as it becomes available. This is the easiest way to mechanize a receiver, but it has significant limitations.
In order to process each sampled bit of input signal sequentially as it becomes available, the typical approach of prior art GPS receivers is to slew the local signals until they match up with the unknown GPS signals; from then on, the signals are tracked using standard phase-locked and delay-locked techniques. The amount of slewing or searching is a function of the uncertainties in the receiver's position, time, satellite position estimates, etc. as well as a function of the receiver's implementation of correlators, SNRs, dwell time algorithms, etc. Hence, there are many factors contributing to the amount of slewing or searching in a typical prior art GPS receiver.
Further, regardless of how the GPS receiver is implemented, all real-time traditional GPS receivers must search, and while they are searching, the signal is not being tracked and measurements are not being made. Such receivers are therefore referred to as “single-mode” GPS receivers, because they are only capable of either searching or tracking at any given time. Further still, prior art GPS receivers include receiver software which must contend with a variety of asynchronous events.
A need therefore exists for a GPS receiver which is not implemented exclusively in the real-time mode. The need further exists for a GPS receiver capable of simultaneously searching and tracking signals, i.e., a “batch-mode” GPS receiver. Additionally, a need also exists for a GPS receiver operated by software which contends with only synchronous interruptions.